Process for the manufacture of hydrofluoroolefins

ABSTRACT

In this invention we are disclosing a process for the synthesis of hydrocchlorofluoro olefins (HCFO) and/or hydrofluoroolefins (HFO). The process is based on the gas phase, noncatalytic fluorination of hydrochlorofluoropropenes to form hydrofluoropropenes.

The present application is a continuation of U.S. application Ser. No.12/664,205 filed Dec. 11, 2009, which claims priority to PatentCooperation Treaty Application Ser. No. PCT/US08/68293 filed Jun. 26,2008 which claims priority to U.S. Provisional Patent Application Ser.No. 60/946,406 filed Jun. 27, 2007.

FIELD OF THE INVENTION

The present invention relates to a process for the manufacture of ahydrofluoropropenes. More particularly, the present invention relates toa process for manufacturing the hydrofluoropropenes such as1,1,1,2-tetrafluoropropene (“HFO-1234yf”) from a chloropropene materialsuch as 1,1,2,3-tetrachloropropene (“HCO-1230xa”). The process comprisestwo reactions, the first being a liquid phase, noncatalytic fluorinationof the hydrochloropropene to form a hydrochlorofluoropropene (HCFO) andthe second a catalyzed gas phase fluorination of thehydrochlorofluoropropene to form a hydrofluoropropene.

BACKGROUND OF THE INVENTION

The Montreal Protocol for the protection of the ozone layer, signed inOctober 1987, mandate the phase out of the use of chlorofluorocarbons(CFCs). Materials more “friendly” to the ozone layer, such ashydrofluorocarbons (HFCs) eg HFC-134a replaced chlorofluorocarbons. Thelatter compounds have proven to be green house gases, causing globalwarming and were regulated by the Kyoto Protocol on Climate Change. Theemerging replacement materials, hydrofluoropropenes, were shown to beenvironmentally acceptable i.e. has zero ozone depletion potential (ODP)and acceptable low GWP. This present invention describes process formanufacturing of hydrofluoroolefins such as hydrofluoropropenes and/orhydrochlorofluoroolefins. The process of the present invention is basedon a multi reaction process including a liquid phase, noncatalyticfluorination and a catalytic gas phase fluorination to produce desirablefluoroolefins.

Methods of preparing hydrofluoroalkenes are known. For example,WO2007/079431 discloses processes for the production of fluorinatedolefins, including hydrofluoropropenes. The processes which are broadlydescribed as a single reaction or two or more reactions involvefluorination of compound of the formula C(X)_(m)CCl(Y)_(n)C(X)_(m) to atleast one compound of formula CF₃CF=HZ, where each X, Y and Z isindependently H, F, Cl, I or Br and each m is independently 1, 2 or 3and n is 0 or 1. The examples and preferred embodiments are disclosemulti-step process such a reaction sequence wherein a feedstock of1,1,2,3 tetrachloropropene (1230xa) is fluorinated in a catalyzed, gasphase reaction to form a compound such as2-chloro-3,3,3-tri-fluoropropene (1233xf). The 2-chloro3,3,3-tri-fluoropropene is⁻ then converted to2-chloro-2,3,3,3-tetrafluoropropane (244bb) via a liquid phase,catalyzed reaction. The 2-chloro-2,3,3,3-tetrafluoropropane is thandehydrochlorinated to 2,3,3,3-tetrafluoropropene (1234yf) via acatalyzed, gas phase reaction.

DESCRIPTION OF THE INVENTION

The present invention provides a process for producing ahydrofluoropropene of the formula C₃ H_((a+x−1))F_(7−(a+x)) where a=0,1,2, 3 or 4, x=0, 1, 2 or 3 and a+x is greater than or equal to 1, from“feedstock” of a tetrachloropropene comprising the steps of:

-   -   a) liquid phase, noncatalytic fluorination of the        tetrachloropropene to form hydrochlorofluoropropene of the        formula C₃ F₃H_((a+x−1))Cl_(4−(a+x)); and thereafter    -   b) gas phase, catalytic fluorination of the        hydrochlorofluoropropene to form a hydrofluoropropene of the        formula C₃ H_((a+x−1))F_(7−(a+x)) preferably        2,3,3,3-tretafluoropropne.

The first step of the present invention relates to liquid phase,uncatalyzed fluorination of a hydrochloropropene to form ahydrochlorofluoropropene of the formula C₃ F₃H_((a+x−1))Cl_(4−(a+x)).The uncatalyzed liquid phase process comprises contacting ahydrochloropropene of the formula C₃ H_((a+x−1))Cl_(7−(a+x)) with HF.The HF to hydrochloropropene molar ratio is from at least about 3 to 1to about 500 to 1, preferably from about 10 to 1 to about 200 tol. Thereaction temperatures can vary from about 20° C. to about 300° C.,preferably from about 50° C. to about 150° C. Operating pressures canrange from about 100 to about 900 psig, preferably from about 250 toabout 700 psig. Residence time is normally from about 1/4 to 24 hours,preferably from about 1/2 hour to about 2 hours. Any unreacted feedstockcan be easily separated from the desired product due to the largedifference in their boiling points. The reaction produces the desiredhydrochlorofluoropropene which is essentially oligomer free. Thereaction vessel is preferably constructed from material resistant to HF,known in the art such 316L stainless steel, Inconel or Hastelloy. Thereaction can be carried out via a continuous or batch process. Theprincipal by-product of this reaction is hydrogen chloride (HCl), whichmay be removed by conventional means known in the art (such asabsorption or distillation). After removal of HCl, the product streamcontains the desired hydrochlorofluoropropene product, such asHCFC-1233xf, and may include co-products and unreacted startingmaterials including but not limited to: HF, pentafluoropropane such as245cb and chlorotetrafluoropropane such as 244bb. This stream providesthe feedstock for the final reaction step.

The final reaction step of the present invention relates a gas phase,catalytic fluorination of the hydrochlorofluoropropene from the firstreaction step, to form a hydrofluoropropene of the formula C₃H_((a+x−1))F_(7−(a+x)). The process involves contacting thehydrochlorofluoropropene with HF in a first reaction zone underconditions sufficient to produce a three carbon hydrofluoroolefin of theformula C₃ H_((a+x−1))F_(7−(a+x)). The HF: hydrochlorofluoroolefm molarratio is typically from about 0.5:1 to 40:1, but is preferably at leastabout 1:1 to enhance conversion and preferably no more than about 10:1in order to produce lower levels of HF which are recovered downstream.Temperatures of from about 250° C. to about 600° C. are typically used,preferably from about 300° C. to about 500° C. Pressures are typicallyfrom about atmospheric to about 400 psig, preferably from about 50 to200 psig. Co-products formed such as 245cb and/or 244bb can be recycledback to the gas phase reactor.

A variety of fluorination catalysts can be used, such as aluminumfluoride or a chromium-based catalyst (such as chromium oxide, Cr₂ O₃),which chromium-based catalyst is either unsupported or supported. Thesupport is selected from fluorided alumina, activated carbon and thelike. The chromium catalyst being used alone or in the presence of aco-catalyst such as zinc, manganese, cobalt or nickel. Three suchpreferred chromium catalysts are pure chromium oxide, chromium/nickelwith nickel co-catalyst and chromium/nickel supported on fluorinatedalumina. Preparation of this latter catalyst being disclosed, forexample, in U.S. Pat. No. 5,731,481. The chromium-based catalysts arepreferably activated before use, typically by a procedure wherein thecatalyst bed is heated to about 370°-380° C. (normally with a continuousflow of nitrogen), after which a mixture of approximately equal volumesof HF and air or nitrogen (preferably nitrogen) are fed over thecatalyst bed for about 18 hours at higher pressure, varied between100-200 psig. US 2007/0299286 sets out a suitable catalyst activationprocess.

An oxygen, oxygen containing compound, chlorine, or other oxidizer canbe used as a co-feed to extend the catalyst lifetime, typically in anamount of from about 0.005 to about 1 mole% of chlorine or oxygen permole of organic in the feed. The oxygen being introduced as anoxygen-containing gas such as air, oxygen, or an oxygen/nitrogenmixture. Contact times (catalyst volume divided by the total flow rateof reactants and cofeeds at the operating temperature and pressure ofthe process) are preferably from about 1 to about 250 seconds, morepreferably from about 1 to about 50 seconds.

The reaction product of the gas phase, catalytic fluorination step willinclude, in addition to the desired hydrofluoropropene, unreactedhydrochlorofluoropropene, and fluro- and chlorofluor-substituted propanesuch as 245cb and 244bb. These byproducts can be separated from thedesired hydrofluoropropene in a series of two or more separation columnswith the by products being recycled to the gas phase, catalyticfluorination reaction.

The tetrachloropropene feedstock of the present invention can be formedvia variety of ways as would be know by a person skilled in the art.

EXAMPLES

The data presented in the examples was calculated based upon resultsobtained in comparable reactions with closely related materials.

Examples 1

Uncatalyzed liquid phase fluorination of 1,1,2,3 tetrachloropropene(HCO-1230xa) to 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf).

CCl₂=CCl(CH₂Cl)+3HF→CF₃CCl=CH₂+3HCl

0.28 moles of HCO-1230xa can be loaded into a 300 ml Hastelloy Cautoclave equipped with gas inlet valve, mechanical stirrer and anoutlet cooling tower. 3.5 moles of HF gas can be condensed in theautoclave. The reaction mixture would be gradually heated up to 120° C.,with continuous stirring for approximately 1/2 hour. Excessive gaspressure resulted from the formation of HCl can be vented through a 400psi pressure relief valve on the cooling tower. The high boilingmaterial would be trapped at room temperature. The volatile organicproducts could be dried over anhydrouS calcium sulfate and collected ina cold trap. Nearly 0.28 moles of the 2-chloro-3,3,3-trifluoropropeneproduct, would be found in the cold trap. Examples 1, 2 and 3,summarized in Table 1, were calculated based upon comparable reactionswith closely related materials.

TABLE 1 Summary of the results, uncatalyzed liquid phase fluorination of1230xa to 1233xf Example 1 Temperature 100 ° C. Pressure 300 psig MoleRatio 166 HF/1230za Residence 5 time, hours % Conversion 100 1230xa %1234yf 0.25 % 245cb 0.16 % 1233xf 97.2 Other 2.39 1234yf is CF₃CF═CH₂245cb is CF₃CF₂CH₃ 1233xf is CF₃CCl═CH₂ 244bb is CF₃CFClCH₃

Examples 2-4

Gas phase fluorination of HCO-1233xf at high temperature.

An activated catalyst, 15cc, could be loaded into a vertical fix bedreactor (20 inches by 1 inch Hastelloy C). HF could be fed as a liquid,and converted to a gas using vaporizer. HCO-1233xf could be fed to thefix bed reactor using a syringe pump and heated up to 365° C. Thereaction would be run at a pressure of between 42-162 psi. Table 3summarizes the calculations of expected results using a variety of molarratio of HCO-1233xf/HF and contact times based upon comparable reactionswith closely related materials.

TABLE 3 Summary of fluorinating 1233xf to 1234yf, using unsupportedCr₂O₃ catalyst Example 2 3 4 Temp ° C. 365 365 365 Pressure psig 48.548.5 169 O₂/1233xf ratio 0.5 0.5 0.5 HF/1233xa 10.6 21.1 21.1 MolarRatio Contact Time sec. 3.9 4 14 % Conversion 54.8 64.1 73.6 % 1234yf58.3 56.4 40.6 % 245cb 36.6 36.5 59.4 % 244bb 5.1 7.1 0 1234yf isCF₃CF═CH₂ 245cb is CF₃CF₂CH₃ 244bb is CF₃CFClCH₃

While the present invention has been described with respect toparticular embodiments thereof, it is apparent that numerous other formsand modifications of this invention will be obvious to those skilled inthe art. The appended claims and this invention generally should beconstrued to cover all such obvious forms and modifications which arewithin the true spirit and scope of the present invention.

1. A process for producing a hydrofluoroolefm of the formula C₃H_((a+x−1))F_(7−(a+x)) where a=0,1, 2, 3 or 4 and x=0, 1, 2 or 3 and a+xis greater than or equal to 1, comprising the step of: a) fluorinating ahydrochlorofluoroolefm of the formula C₃ F₃H_((a+x−1))Cl_(4−(a+x)) in agas phase, in the presence of a suitable catalyst to form ahydrofluoroolefin of the formula C₃ H_((a+x−1))F_(7−(a+x)) andco-products.
 2. The process of claim 1 further comprising the step of:separating said co-products from said hydrofluoroolefin.
 3. The processof claim 1 wherein said co-products comprise pentafluoropropane andchlorotetrafluoropropane.
 4. The process of claim 3 wherein saidpentafluoropropane comprises HFC-245cb and said chlorotetrafluoropropanecomprises HCFC-244bb.
 5. The process of claim 1 wherein the temperatureranges from about 250° C. to about 600° C.
 6. The process of claim 1wherein the temperature ranges from about 300° to about 500° C.
 7. Theprocess of claim 1 wherein the pressure ranges from about atmospheric toabout 400 psig.
 8. The process of claim 1 wherein the pressure rangesfrom about 50 to about 200 psig.
 9. The process of claim 1 wherein thestep of fluorinating the hydrochlorofluoroolefm in a gas phase, in thepresence of a suitable catalyst comprises contacting saidhydrochlorofluoroolefin with hydrogen fluoride in the presence of asuitable catalyst.
 10. The process of claim 9 wherein said catalyst is achromium catalyst supported or unsupported.
 11. The process of claim 9wherein said process further comprises a co-catalyst.
 12. The process ofclaim 11 wherein said co-catalyst is selected from nickel, zinc, cobaltor manganese.
 13. The process of claim 9 wherein said catalyst isactivated prior to use.
 14. The process of claim 13 wherein saidcatalyst is activated at a pressure above about 150 psi prior to use.15. The process of claim 1 wherein said hydrochlorofluoroolefin is2-chloro-3,3,3-trifluoro-1-propene and said hydrofluroolefin is2,3,3,3-tetrafluoro-1-propene.